\documentclass{article}
\usepackage{amsmath}
\begin{document}
\pagestyle{empty}
\begin{alignat*}{2}
p&=0 &\hspace{65pt} 0 \le x &<n\\
p&=1 & n \le x &<2n\\
p&=2 & 2n \le x &<3n\\
p&=3 & 3n \le x &<4n+1\\
p&=4 & 4n+1 \le x &<(4n+1)+n\\
p&=7 & (4n+1)+3n \le x &<2(4n+1)\\
\end{alignat*}
\end{document}
